Studies of the plasma lipoproteins of patients with familial LCAT deficiency will be continued to provide additional information concerning the role of lecithin: cholesterol acyltransferase in cholesterol transport. In particular, two lipoprotein fractions, not hitherto characterized, will be analyzed. These lipoproteins, both obtained in the density class of d 1.063-1.25 g/ml, are: (1) One that is rich in Beta-peptide and (2) one that appears mainly to contain the so-called "arginine-rich" peptide. In addition, the A-peptide-containing lipoproteins in the same lipoprotein class will be studied, particularly to test a new hypothesis concerning aspects of the mechanism of the lecithin-cholesterol acyltransferase reaction.